Remove the obj, xobj and src directories from the base set.

The installer will create these directories during install.
So local setups will not get overwritten during upgrades.
idea from and OK deraadt@
with help from and OK tb@
feedback from and no objections halex@

src/etc/Makefile

@@ -1,4 +1,4 @@
-#	$OpenBSD: Makefile,v 1.443 2016/10/14 18:45:12 deraadt Exp $
+#	$OpenBSD: Makefile,v 1.444 2016/11/05 09:14:37 rpe Exp $
 
 TZDIR=		/usr/share/zoneinfo
 LOCALTIME=	Canada/Mountain
@@ -228,15 +228,6 @@ distrib-dirs:
 		${INSTALL} -d -o root -g wheel -m 755 ${DESTDIR}; \
 	fi
 	mtree -qdef mtree/4.4BSD.dist -p ${DESTDIR}/ -U
-	if [ ! -d ${DESTDIR}/usr/src ]; then \
-		${INSTALL} -d -o root -g wsrc -m 775 ${DESTDIR}/usr/src; \
-	fi
-	if [ ! -d ${DESTDIR}/usr/obj ]; then \
-		${INSTALL} -d -o root -g wsrc -m 775 ${DESTDIR}/usr/obj; \
-	fi
-	if [ ! -d ${DESTDIR}/usr/xobj ]; then \
-		${INSTALL} -d -o root -g wsrc -m 775 ${DESTDIR}/usr/xobj; \
-	fi
 	cd ${DESTDIR}/; ln -fhs usr/src/sys sys
 	chown -h root:wheel ${DESTDIR}/sys